The future of one of the world's largest ocean sanctuaries is in doubt following the change of government in New Zealand.

The 620,000 square kilometre Kermadec Ocean Sanctuary, between New Zealand and Tonga, was announced by then Prime Minister John Key at the United Nations in 2015, and was hailed around the world.

But now the minority New Zealand First Party has insisted that it's larger coalition partner, Labour, agree to not proceed with legislation establishing the sanctuary in its first term while outstanding issues are resolved.